The invention relates to an apparatus and a method for depleting CO2, from breathing gas using hydroxide compounds and moisture-absorbing substances.
Closed and semi-closed breathing circuits serve to allow the user breathing wholly or partially independent from ambient air. This is true, for example, for circuit breathing apparatuses of firefighters, for mines, but also for escape devices, diving equipment or submarines. By circulating the respiratory air breathing gas can be saved. This is particularly important for use in anesthesia. It is necessary, however, to deplete carbon dioxide produced and exhaled by the user.
Depleting carbon dioxide is generally accomplished by alkali or alkaline earth metal hydroxides with a variety of additives. For example, according to the following reaction schemes:CO2+H2O→H2CO3 H2CO3+2NaOH→Na2CO3+2H2ONa2CO3+Ca(OH)2→CaCO3+2NaOHCa(OH)2+CO2→CaCO3+H2O+heat AHR=−113 kJ/mol
Alkaline earth metal hydroxides used in such a manner are often referred to soda lime. Besides alkaline earth metal hydroxides, water is reactant, which is needed for optimum reactivity of the CO2 absorber.
For use in anesthesia already several absorption materials have been proposed. Known absorption materials are often alkaline earth metal chlorides (EP 0939671 B1, WO 98/23370), simple silicates or also alkaline earth metal sulfates (EP 0939671 B1). For the purposes of the present invention, it is necessary to achieve a higher absorption capacity for carbon dioxide, in particular when using moist gases.
It has been discovered that the addition of conventional humectants can lead to losses in the absorption capacity for acid gases of the absorber, and to a reduction in abrasion resistance.
When storing soda lime, water can be lost through the packaging. This may decrease the CO2 absorption capacity, because water is no longer available as reactant in sufficient quantity (see reaction schemes above). Additionally, during transportation in the respective packaging there may be abrasion (dust) of the soda lime. This dust is undesirable as it will be, without appropriate countermeasures, present in the breathing circuit and included therein.
The object of the invention is to provide absorption material for acid gases, without the disadvantages of the prior art and, in particular, on the one hand, providing water and, on the other hand, binding water, and being storage-stable, i.e., the absorption performance of the absorber over the storage period is maintained, without loss of CO2 absorption capacity. A simultaneous increase in abrasion resistance is also desirable.
This object is achieved by the subject matter of the independent claims. Preferred embodiments are subject of the dependent claims, or are described below.